Microphone device and system comprising the microphone device

ABSTRACT

There is described a switchable microphone device which may be switched between a digital output mode and an analog output mode. There is further described a system for use of such a device, which allows for the switching between analog and digital computing modes.

The present disclosure claims priority to United States ProvisionalPatent Application Ser. No. 62/768,180, filed on Nov. 16, 2018, U.S.Provisional Patent Application Ser. No. 62/801,931, filed on Feb. 6,2019, and United Kingdom Patent Application No. 1903809.0, filed on Mar.20, 2019, each of which is incorporated by reference herein in itsentirety.

BACKGROUND

Embodiments of the present disclosure relate to switchable microphonedevice and a system incorporating the switchable microphone device.

Increasing numbers of electronic devices are now being provided withembedded microphones, including personal audio devices such as mobilephones, tablet computers, music players, etc., as well as so-called“smart devices”, such as voice assistant devices or electronic deviceshaving embedded voice-processing functionality, e.g. smart televisions,home music players, etc. Such electronic devices are often provided withalways-on listening capability.

Particularly for portable battery-powered devices, there is a continueddesire to reduce the overall power consumption of such devices, whilesimultaneously not significantly impacting on device performance.

It is an object of embodiments of the present disclosure to provide amicrophone device and system which addresses the above.

SUMMARY

Accordingly, there is provided a switchable microphone devicecomprising:

-   -   an input to receive at least one input analog sensor signal        indicative of sound pressure received by a transducer;    -   an analog-to-digital converter (ADC) to convert the input analog        sensor signal to a converted digital signal; and    -   a controller to switch the device between:        -   a digital output mode, where the switchable microphone            device outputs a digital microphone output signal based on            the converted digital signal; and        -   an analog output mode, where the switchable microphone            device outputs an analog microphone output signal based on            the input analog sensor signal.

By allowing for the switching between analog and digital output modes,the switchable microphone device may be effectively used in systemshaving both analog and digital processing solutions. In addition,providing an analog output mode may allow for digital processing aspectsof the device to be powered-down or made inactive, reducing the powerconsumption of the device itself.

In a preferred aspect, the device comprises a transducer which isconfigured to provide an input analog sensor signal indicative of soundpressure received by the transducer. In such an embodiment, it will beunderstood that the switchable microphone device may be provided as asingle package, e.g. as a co-packaged microphone element, which may beintegrated with a larger circuit system. In some embodiments, the devicemay be provided with multiple microphone transducers configured toprovide a plurality of input analog sensor signals, wherein the multiplemicrophone transducers are optimised for a particular amplitude and/orfrequency range of the received sound pressure.

The co-packaged element may be provided with the transducer and theswitching elements on a common die, or with the transducer provided on adie separate to the switching elements within a common package.

Preferably, the device is arranged to receive a control signal, whereinthe controller switches between the digital and analog output modesbased on the received control signal.

In a preferred aspect, the controller is further configurable to switchthe device to:

-   -   a hybrid output mode, where the switchable microphone device        outputs both the digital microphone output signal based on the        converted digital signal, and the analog microphone output        signal based on the input analog sensor signal.

By providing such a third output mode, the device may allow for bothanalog and digital output signals from the microphone, which may be usedfor downstream signal processing of both the analog and digital signals.

In some embodiments, it will be understood that the device may beconfigured to output the analog microphone output signal when the deviceis in the digital output mode.

Preferably, the device is arranged to receive a clock signal for theADC, wherein the clock signal operates as the control signal to controlthe switching of the output modes of the device.

Using a clock signal as a control signal allows for total pin count forthe device to be reduced.

In one aspect, the controller is arranged to monitor the received clocksignal, wherein the controller switches the device to the analog outputmode if the clock signal is retained at a high value or at a low valueexceeding a threshold time period.

It will be understood that the threshold time period may be selected tobe longer than a predefined cycle time or half cycle for the ADC. Itwill be understood that the predefined cycle time may allow for drift inthe exact ADC cycle time, and/or allow for the ADC to be able to operatein different modes based on the supplied clock frequency.

The clock signal may be configured to be held low or held high by anexternal driver. Additionally or alternatively, the device may beprovided with a pull-up or pull-down element as required, e.g. aresistor or similar load device, or a suitably-configured transistore.g. a MOSFET, to force the clock signal to a high or low value in theevent of the external clock signal being in a high-impedance state.

Preferably, the controller may be configured to switch the device to thedigital output mode if the received clock signal is within an allowedfrequency range.

The allowed frequency range may be a defined frequency range for ADCoperation, which may be defined to allow for variations in ADC operatingfrequency, and/or drift in exact cycle frequency of the ADC.

Alternatively, the device may be provided with a control input separateto a clock input, where the control input controls the switching of theoutput modes of the device.

Preferably, the device further comprises amplifier circuitry to providea buffered analog output signal based on the input analog sensor signal.

The amplifier circuitry may be used to ensure that an analog output fromthe microphone device is sufficient to meet the requirements of anyoff-device loads to receive the analog output signal. Additionally oralternatively, the use of such amplifier circuitry may buffer arelatively weak signal from the transducer for further processing.

In one aspect, the ADC is configured to convert the buffered analogoutput signal to the converted digital signal.

Alternatively, the ADC may be configured to convert the input analogsensor signal directly. Such an ADC may comprise a built-in buffer oramplifier.

In one aspect, the amplifier circuitry comprises one or more of thefollowing:

-   -   an adjustable gain amplifier;    -   a signal compression function; or    -   an analog filtering module.

The amplifier circuitry can be configured to adjust the gain of theanalog signal; to perform a compression of the analog signal, e.g. alogarithmic or standard compand function; or to perform a filtering ofthe analog signal, e.g. a high-pass, low-pass, or band-pass filtering ofthe signal.

Preferably, the device further comprises an output interface to providea digital microphone output signal based on the converted digitalsignal.

Preferably, the device further comprises a digital signal processingmodule arranged to perform digital signal processing on the converteddigital signal to provide a processed digital signal, and the digitalmicrophone output signal may be based on the processed digital signal.

Examples of digital signal processing which may be performed in themicrophone device may include:

-   -   noise reduction of the converted digital signal;    -   wind noise suppression of the converted digital signal;    -   filtering of the converted digital signal; and    -   data formatting of the digital signal.

Preferably, the device comprises:

-   -   a digital output interface to output the digital microphone        output signal; and    -   an analog output interface to output the analog microphone        output signal.

In one embodiment, the device comprises a common output pin, wherein thecontroller controls the driving of the common output pin by the digitaloutput interface and the analog output interface.

By providing a common output pin, the device may be configured to have alower pin count, which can provide advantages in space-saving androuting of external signals. The controller may be configured to switchbetween the digital output interface and the analog output interfacebeing connected to the common output pin, or the controller maytri-state the output signals of the digital output interface and theanalog output interface as appropriate.

In an alternative aspect, the digital output interface comprises a bus,such as a single-wire or multiple-line bus, for the provision of aparallel bus output, e.g. a SLIMbus® output or a SoundWire® interface.Such a system may be used as a multi-drop bus, wherein the digitaloutput of the device may be provided to multiple downstream devices.

In such an embodiment, the analog output interface comprises at leastone analog output pin, the at least one analog output pin separate fromthe multiple-line bus.

In addition, the provision of a separate analog output pin may allow forthe operation of a hybrid output mode, where the switchable microphonedevice outputs both the digital microphone output signal based on theconverted digital signal, and the analog microphone output signal basedon the input analog sensor signal.

Preferably, the device comprises a plurality of digital signal paths forthe input analog sensor signal to provide a converted digital signalhaving a high dynamic range, the digital signal paths each comprisingamplifier circuitry and an ADC,

-   -   wherein the amplifier circuitry of the different paths is        configured to provide different signal ranges of the input        analog sensor signal, and wherein the outputs of the ADCs of the        different paths are combined to provide a converted digital        signal having a high dynamic range.

For example, the different digital paths may comprise a first,approximately unity-gain, path to provide an analog signal with a“regular” range of operation, and a second, reduced-gain, path toprovide an analog signal having a higher range to accommodate analogsignals which may saturate any amplifiers tuned for a “regular” range ofoperation.

In one aspect, the analog microphone output signal is based on acombined version of the outputs of the amplifier circuitry of thedifferent paths.

Alternatively, the analog microphone output signal is based on onesignal range of the input analog sensor signal. In such a configuration,the analog microphone output signal may be based on the analog signal inthe “regular” path.

An example of a dual-path front-end configuration can be found in U.S.Pat. No. 6,271,780, the contents of which are incorporated by referenceherein.

There is further provided a system comprising:

-   -   a switchable microphone device as described above; and    -   a processor configured to control switching of the microphone        device between the digital output mode and the analog output        mode, the processor arranged to control processing of the output        of the microphone device.

The system may be provided as a battery-powered personal audio devicesuch as a mobile phone, a tablet computer, a personal music player, etc.The system may also be provided as a “smart device”, such as a voiceassistant device, or an electronic device having embeddedvoice-processing functionality, e.g. smart televisions, home musicplayers, etc. The processor may be provided as an applications processor(AP) or a central processing unit (CPU) of such a device. The processormay be arranged to receive the output of the switchable microphonedevice, or the processor may be configured to control the routing of theoutput of the switchable microphone device to additional processingmodules of the system.

Preferably, the processor controls a clock signal provided to themicrophone device to control the mode switching of the microphonedevice. Alternatively, the processor may control a control signalprovided to the microphone device to control the mode switching of themicrophone device.

Preferably, the system further comprises:

-   -   an analog signal processing module, the analog signal processing        module arranged to receive an analog microphone output signal        from the switchable microphone device; and    -   a digital signal processing module, the digital signal        processing module arranged to receive a digital microphone        output signal from the switchable microphone device.

The analog and digital signal processing modules are arranged to processaudio received by a transducer. The analog signal processing module maycomprise an analog machine learning system. Preferably, the analogsignal processing module is configured for relatively low-power,always-on computing. The digital signal processing module may comprise aDSP or a digital machine learning system. Preferably, the digital signalprocessing module is configured for relatively high-performance,high-accuracy computing. It will be understood that the processingmodules may be provided as part of the processor of the system, or maybe provided as discrete processing units the operation of which may becontrolled by the processor of the system.

Preferably, the processor is arranged to switch the system between:

-   -   an analog computing mode, wherein the microphone device is        switched to the analog output mode to provide the analog        microphone output signal to the analog signal processing module;        and    -   a digital computing mode, wherein the microphone device is        switched to the digital output mode to provide the digital        microphone output signal to the digital signal processing        module.

In some embodiments, it will be understood that the microphone devicemay continue to output the analog microphone output signal when themicrophone device is switched to the digital output mode.

Preferably, the system is further configured such that:

-   -   when in the analog computing mode, the processor is configured        to maintain the digital signal processing module in an inactive        or low-power state; and    -   when in the digital computing mode, the processor is configured        to maintain the analog signal processing module in an inactive        or low-power state.

In a further embodiment, the processor is arranged to further switch thesystem to:

-   -   a hybrid computing mode, wherein the microphone device is        switched to a hybrid output mode to provide the analog        microphone output signal to the analog signal processing module,        and to provide the digital microphone output signal to the        digital signal processing module.

In such a hybrid computing mode, the analog and digital signalprocessing modules may operate in parallel, with the outputs of bothmodules fused or combined by the processor. While the digital signalprocessing module may be configured to provide relatively higheraccuracy than the analog signal processing module, the analog signalprocessing module may be configured to provide a faster response time.In such a configuration, the fusion of the outputs of both the analogand digital signal processing modules may provide an improvement inperformance of the overall system.

Alternatively, for embodiments where the microphone device continues tooutput the analog microphone output signal when the microphone device isswitched to the digital output mode, the system is configured such that:

-   -   when in the analog computing mode, the processor is configured        to maintain the digital signal processing module in an inactive        or low-power state; and    -   when in the digital computing mode, the processor is configured        to activate both to maintain the analog signal processing module        and the digital signal processing module.

Preferably, the processor switches the system from the analog computingmode to the digital computing mode based on one or more of thefollowing:

-   -   a user input, such as a mechanical button press;    -   a voice activity detection module (VAD) indicating the presence        of speech in received audio;    -   a voice keyword detection module (VKD) indicating the presence        of a keyword or wake-word in received audio;    -   a speaker identification or verification module indicating the        identity or authorisation of a speaker of the received audio;        and    -   a command recognition module arranged to recognise commands        present in speech in the received audio.

The system may change between the different operational modes based onprocessing requirements. In a preferred aspect, the system operates in arelatively low-power, always-on mode utilising the analog computing modeuntil there is a requirement for a higher accuracy output which mayrequest a transition to the digital computing mode. For always-on audiolistening applications, e.g. for speaker identification or verification,or automatic speech recognition, the transition may be triggered as aresult of the system detecting the presence of voice or speech in thereceived audio, or the presence of a spoken keyword or wake-word in thereceived audio. It will be understood that such a VAD or VKD output maybe provided by the output of the analog signal processing module, whichmay operate in an always-on mode.

In a further aspect, the system may be triggered to transition from theanalog to the digital computing mode based on the output of a speakeridentification or verification process. In particular, the system may beconfigured to perform an always-on speaker identification orverification process on the received audio using the analog signalprocessing module, and wherein the system is transitioned to the digitalcomputing mode if the analog signal processing module identifies orverifies a speaker in the received audio. In some aspect, the digitalsignal processing module may then be used to perform further speakeridentification or verification on the received audio, and/or to performspeech or command recognition on the received audio.

Preferably, the processor switches the system from the digital computingmode to the analog computing mode based on one or more of the following:

-   -   a user input, e.g. an indication to power-down the system;    -   the processor determining that a session has ended; and    -   a system time-out.

The processor may act to transition the system back to the analogcomputing mode from the digital computing mode based on any suitableparameters.

While the above-described features relate to a microphone device and thesignals produced by microphone transducers, it will be understood thatthe same principles and features may be applied for alternative devices,having other types of transducers where it may be desired to provideswitchable analog and digital output modes, for example opticaltransducers, capacitive transducers, force sensing transducers,inductive sensing transducers, proximity detection transducers,ultrasonic transducers.

Accordingly, there is provided a switchable transducer devicecomprising:

-   -   an input to receive an input analog sensor signal from a        transducer;    -   an analog-to-digital converter (ADC) to convert the input analog        sensor signal to a converted digital signal; and    -   a controller to switch the device between:        -   a digital output mode, wherein the switchable transducer            device outputs a digital output signal based on the            converted digital signal; and        -   an analog output mode, wherein the switchable transducer            device outputs an analog output signal based on the input            analog sensor signal.

There is further provided a system comprising:

-   -   a switchable transducer device as described above; and    -   a processor configured to control switching of the transducer        device between the digital output mode and the analog output        mode, the processor arranged to control processing of the output        of the transducer device.

Additionally or alternatively, it will further be understood that asystem may be provided with an output of a microphone device differentto the switchable microphone device described above.

Accordingly, there is further provided a system comprising:

-   -   at least one microphone device to provide a microphone signal        indicative of sound pressure received by a transducer of the        microphone;    -   an analog signal processing module, the analog signal processing        module arranged to receive an analog microphone signal from a        microphone device;    -   a digital signal processing module, the digital signal        processing module arranged to receive a digital microphone        signal from a microphone device; and    -   a processor arranged to control switching of the system between:        -   an analog computing mode, wherein the analog signal            processing module is enabled and the digital signal            processing module is maintained in a low-power or inactive            state; and        -   a digital computing mode, wherein the digital signal            processing module is enabled and the analog signal            processing module is maintained in a low-power or inactive            state.

The analog and digital signal processing modules are arranged to processaudio received by a microphone transducer.

The analog and digital signal processing modules may be configured toperform one or more of the following:

-   -   a voice activity detection process (VAD) indicating the presence        of speech in received audio;    -   a voice keyword detection process (VKD) indicating the presence        of a keyword or wake-word in received audio;    -   a speaker identification or verification process indicating the        identity or authorisation of a speaker of the received audio;    -   a speech recognition process arranged to recognise speech in the        received audio; and    -   a command recognition process arranged to recognise commands        present in speech in the received audio.

Preferably, the analog signal processing module comprises an analogmachine learning system. Preferably, the analog signal processing moduleis configured for relatively low-power, always-on computing.

Preferably, the digital signal processing module comprises a digitalmachine learning system. Preferably, the digital signal processingmodule is configured for relatively high-performance, high-accuracycomputing.

Preferably, the processor is arranged to further control switching ofthe system between:

-   -   a hybrid computing mode, where both the analog signal processing        module and the digital signal processing module are enabled.

In a further aspect, there is provided a system comprising:

-   -   a switchable microphone device as described above; and    -   a downstream processing unit coupled to the switchable        microphone device so as to receive the analog microphone output        signal,    -   wherein the downstream processing unit comprises a second analog        to digital converter (ADC) operative to convert the received        analog microphone output signal to a supplementary converted        digital signal, wherein the second ADC has a higher bandwidth        than the ADC of the switchable microphone device, such that a        bandwidth of the supplementary converted digital signal is        greater than a bandwidth of the digital microphone output signal        output by the switchable microphone device, and    -   wherein the system is configured to enable the second ADC if the        converted digital signal output by the ADC of the switchable        microphone device is indicative that the input analog sensor        signal contains particular audio content.

The system may further comprise a controller configured to receive theconverted digital signal output by the ADC of the switchable microphonedevice and to enable the second ADC if the converted digital signaloutput by the ADC of the switchable microphone device is indicative thatthe input analog sensor signal contains particular audio content.

The downstream processing unit may be coupled to the switchablemicrophone device so as to receive the digital microphone output signal.

The downstream processing unit may further comprise a combiner tocombine the digital microphone output signal and the supplementaryconverted digital signal to generate a full-bandwidth digital signal.

Alternatively, the second ADC may be configured such that a bandwidth ofthe second ADC encompasses a bandwidth of the ADC of the switchablemicrophone device, such that the bandwidth of the supplementaryconverted digital signal encompasses the bandwidth of the digitalmicrophone output signal output by the switchable microphone device.

The particular audio content may comprise speech.

The particular audio content may comprise a trigger word or phrase.

The downstream processing unit may further comprise an analog signalbuffer configured to store the analog microphone output signal receivedfrom the switchable microphone device over a predetermined period oftime.

In a still further aspect, there is provided a switchable microphonedevice comprising:

-   -   an input to receive an input analog sensor signal indicative of        sound pressure received by a transducer;    -   a first analog-to-digital converter (ADC) to convert the input        analog sensor signal to a first converted digital signal;    -   a second ADC to convert the input analog sensor signal to a        second converted digital signal, wherein the second ADC has a        higher bandwidth than the first ADC such that a bandwidth of the        second converted digital signal is greater than a bandwidth of        the first converted digital signal,    -   wherein the switchable microphone device is configured to enable        the second ADC if the first converted digital signal is        indicative that the input analog sensor signal contains        particular audio content.

The device may further comprise a controller configured to receive thefirst converted digital output signal and to enable the second ADC ifthe first converted digital signal is indicative that the input analogsensor signal contains particular audio content.

The device may further comprise a combiner to combine the firstconverted digital signal and the second converted digital signal togenerate a full-bandwidth digital output signal.

The particular audio content may comprise speech.

Alternatively, the particular audio content may comprise a trigger wordor phrase.

The device may further comprise at least one microphone transducerconfigured to provide the input analog sensor signal indicative of soundpressure received by the at least one microphone transducer.

The device may further comprise amplifier circuitry configured to outputa buffered analog output signal based on the input analog sensor signal.

The device may further comprise an analog signal buffer configured tostore the buffered analog output signal output by the amplifiercircuitry over a predetermined period of time.

The first DAC may be provided in a digital signal path between the inputand an output interface of the device.

The second DAC may be provided in an analog signal path between theinput and an output interface of the device, wherein the analog signalpath is configured to provide an analog output signal to the outputinterface when the second DAC is disabled.

In a further aspect, there is provided a system comprising:

-   -   a switchable microphone device a; and    -   a processor,    -   wherein the processor is configured to receive the first        converted digital signal and to issue a control signal to the        switchable microphone device to enable the second ADC if the        first converted digital signal is indicative that the input        analog sensor signal contains particular audio content.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is an illustration of a first embodiment of a microphone deviceaccording to the present disclosure;

FIG. 2 is a cross-sectional view of a packaging configuration of themicrophone device according to the present disclosure;

FIG. 3 is a cross-sectional view of an alternative packagingconfiguration of the microphone device according to the presentdisclosure;

FIG. 4 is an illustration of a second embodiment of a microphone deviceaccording to the present disclosure;

FIGS. 5(a)-(c) are illustrations of further embodiments of a microphonedevice according to the present disclosure, which allow for high dynamicrange output signals;

FIG. 6 is an illustration of a first configuration of an outputinterface for the microphone device according to the present disclosure;

FIG. 7 is an illustration of a second configuration of an outputinterface for the microphone device according to the present disclosure;

FIG. 8 is an illustration of a system incorporating a microphone deviceaccording to an aspect of the present disclosure;

FIG. 9 is an illustration of a system incorporating a switchabletransducer device according to a further aspect of the presentdisclosure;

FIG. 10 is an illustration of a further system incorporating amicrophone device according to an aspect of the present disclosure; and

FIG. 11 is an illustration of a further embodiment of a microphonedevice according to the present disclosure.

DETAILED DESCRIPTION

With reference to FIG. 1, an embodiment of a switchable microphonedevice 10 according to the present disclosure is shown.

The device 10 is provided with a microphone transducer 12 which isarranged to provide an input analog sensor signal indicative of soundpressure received by the transducer 12. The analog sensor signal isprovided to amplifier circuitry 14 which is configured to buffer, boost,and/or condition the received input analog signal. The buffered outputof the amplifier circuitry 14 is provided to an analog-to-digitalconverter (ADC) 16, which converts the analog signal into a digitalsignal. It will be understood that the ADC 16 may be arranged to receivea clock signal to clock the operation of the ADC 16. Such a clock signalmay be provided from an on-device oscillator, and/or may be receivedfrom or derived from an external clock signal.

The converted digital signal provided by the ADC 16 may comprise amulti-line or multi-wire output digital signal, or may comprise amodulated single-wire digital signal, e.g. a pulse-width-modulated (PWM)signal or pulse-density modulated (PDM) signal. The converted digitalsignal from the ADC 16 is provided to an output interface 18, which isconfigured to output a digital microphone output signal from theswitchable microphone device 10 to downstream processing modules.

In addition to the above-described digital signal path which providesthe converted digital signal, the switchable microphone device 10further comprises an analog signal path, wherein the output of theamplifier circuitry 14 is also provided to the output interface 18, asan analog microphone output signal for transmission to downstreamprocessing modules.

The switchable microphone device 10 further comprises a controller 20,which is operable to switch the device 10 between two modes:

-   -   a digital output mode, where the device 10 outputs the digital        microphone output signal based on the converted digital signal;        and    -   an analog output mode, where the device 10 outputs an analog        microphone output signal based on the input analog sensor        signal.

Analog computing systems may provide an advantage over digital systems,by virtue of their reduced power consumption. However, digital systemsmay be more easily constructed for relatively complicated andhigh-accuracy processes. In such a situation, it is recognised thatthere is a potential need for computing systems having both analog anddigital computing systems, which accordingly require both analog anddigital input signals. Such hybrid processing solutions may provideparticular advantages in audio processing devices, where there may be arequirement to have an initial relatively low-power always-on listeningstate, which may power-gate a relatively high-power, high-accuracyprocessing state.

By providing a switchable microphone device, accordingly a single devicecan provide both the analog and digital signals for any such downstreamprocessing modules.

Providing a single microphone device that can switch between a digitalor an analog output may allow for a reduction in the overall powerconsumption of a system. For example, when the device is operating inone particular mode, then the components of the other signal path may bedeactivated or maintained in a relatively low-power state to reduce theoverall power consumption of the device. In addition, power consumptionrelated to the driving of external or internal interconnections bysignals having multiple edges may be reduced as required.

In addition, providing a single microphone device that can switchbetween a digital or an analog output provides a device where the outputmay be tailored as required for use in a larger system. For systemshaving a need for both analog and digital microphone outputs, only asingle microphone transducer may be used, which potentially results in areduction in the internal space required for a device, as well as thenumber of external microphone ports required for the device.

The device 10 is configured to receive an external control input 22,which is coupled with the controller 20. The control input 22 is used tocontrol the switching of the device 10 between the analog and digitaloutput modes. In one aspect, the control input 22 may be provided as adedicated control pin or pins provided on the device 10, which instructsthe controller 20 to switch between the output modes as required.

In an alternative aspect, the control input 22 may be provided as aclock signal used for the clocking of the ADC 16. In such an embodiment,the controller 20 may be configured to monitor the frequency of theclock signal control input, and to control the device switching based onthe monitored frequency. For example, if the clock signal is within anallowable frequency range for normal operation of the ADC 16 (forexample in the region of 1-3 MHz), the controller 20 may switch thedevice 10 to a digital output mode to output the converted digitalsignal from the ADC 16.

However, if the monitored frequency is outside of such a frequencyrange, for example if the clock signal is retained at a high value or ata low value exceeding a threshold time period, which may be equivalentto a predefined cycle time or half-cycle for the ADC, then thecontroller 20 may switch the device 10 to an analog output mode tooutput the analog microphone output signal, and to possibly alsodeactivate or place in relatively low-power performance mode thecomponents of the digital signal path to conserve power.

The clock signal may be configured to be held low or held high by anexternal driver. Additionally or alternatively, the device 10 may beprovided with a pull-up or pull-down element as required, e.g. aresistor or similar load device, or a suitably-configured transistore.g. a MOSFET), to force the clock signal to a high or low value in theevent of the external clock signal being in a high-impedance state.

By providing the control input 22 as the clock signal used for theclocking of the ADC 16, accordingly the total pin count and externalconnections for the device 10 may be reduced or minimised.

With reference to FIGS. 2 and 3, it will be understood that theswitching microphone device 10 may be provided as a single packagedelement.

In FIG. 2, a first packaging embodiment of the switching microphonedevice 10 a is shown, where the microphone transducer 12 is provided aspart of a single integrated circuit die 24 with the rest of thecomponents as indicated in FIG. 1.

In FIG. 3, a second packaging embodiment of the switching microphonedevice 10 b is shown, where the microphone transducer 12 is provided asa separate element 12 a connected with an integrated circuit die 26comprising the remainder of the components as indicated in FIG. 1. Inboth embodiments shown in FIGS. 2 and 3, the components are providedwithin a common package 28 for use in a larger electronic system, andare provided with an acoustic port 25 for the microphone transducer 12,and an illustrative output pad or interface 27 which allows for theoutput of signals from the device 10 a,10 b. It will be understood thatthe output pad or interface 27 may comprise any suitable arrangements ofsolder pads or pins or similar, which may be used to connect the device10 a,10 b to a larger circuit. In addition, it will be understood thatthe output pad or interface 27 may be located anywhere on the device 10a,10 b to allow suitable access to the output signals.

In addition to the above-described analog and digital output modes, thecontroller 20 may be further arranged to allow for switching to a thirdoperational mode, called a hybrid output mode, where the switchablemicrophone device 10 outputs both the digital microphone output signaland the analog microphone output signal. The use of such a hybrid outputmode allows for both analog and digital output signals from themicrophone device 10, which may be used for concurrent downstream signalprocessing of both analog and digital signals.

It will be understood that other configurations of switchable microphonedevice may be used. With reference to FIG. 4, a second embodiment ofswitchable microphone device 110 is shown, with elements common to theembodiment of FIG. 1 reproduced with reference numerals increased by100.

In the embodiment of FIG. 4, the analog signal path is provided withadditional analog buffer circuitry 124, which is used to further bufferthe analog output signal from the device 110, and to ensure that ananalog output from the microphone device 110 is sufficient to meet therequirements of any off-device loads to receive the analog outputsignal. The additional analog buffer circuitry 124 may comprise anadjustable gain amplifier, which may be used to provide for anadjustable gain of the analog output signal if required. It will beunderstood that the gain of such an amplifier may be controlled by theintegrated controller 120 and/or by an external control signal. It willbe understood that the adjustable gain amplifier provided in 124 can becontrolled such that the gain of the amplifier is dynamically adjustedto avoid clipping of the analog output signal.

In a further aspect, it will be understood that the analog buffercircuitry 124 may additionally or alternatively comprise a signalcompression function, wherein the analog output signal has reduced gainat relatively large input signals to reduce dynamic range of the outputsignal. Such a compression function may be logarithmic or modelled onstandard compand (compress-expand) functions such as A-law and mu-law.It will be understood that the operation of such a compression functionmay be controlled by the integrated controller 120 and/or by an externalcontrol signal.

In a further aspect, it will be understood that the analog buffercircuitry 124 may additionally or alternatively comprise an analogfiltering module, wherein the analog output signal can be filtered asrequired. Examples of such filtering can include high-pass filtering ofthe analog output signal to remove interferers such as contact noiseand/or acoustic noise from the package; low-pass filtering to removeunnecessary ultrasonic sounds from the analog filtering module; and/or acombination of both high-pass and low-pass filtering.

With reference to FIGS. 5(a)-(c), variations of a third embodiment ofswitchable microphone device 210 a,210 b,210 c are shown, with elementscommon to the embodiment of FIG. 1 reproduced with reference numeralsincreased by 200. The embodiments illustrated in FIGS. 5(a)-(c) aredirected towards switchable microphone devices having high dynamicranges.

In the embodiment of FIG. 5(a), the switchable microphone device 210 ahas a digital signal path which is configured to have a dual-pathfront-end, to allow for the conversion of high-dynamic range signals. Insuch a configuration, a first digital signal path is provided havingfirst amplifier circuitry 214 a and first ADC 216 a, and a seconddigital signal path is provided having second amplifier circuitry 214 band second ADC 216 b. The first amplifier circuitry 214 a is configuredto have approximately normal or unity gain to provide for conversion ofrelatively “normal” audio received by the transducer 212. However,high-amplitude audio may cause amplifier 214 a or ADC 216 a to clip orsaturate. Accordingly, the second amplifier circuitry 214 b isconfigured to have a reduced gain, e.g. −20 dB, such that anyhigh-amplitude audio received by the transducer 212 does notover-saturate the second ADC 216 b. The subsequent outputs of the firstand second ADCs 216 a,216 b may be selected or mixed to provide theresultant converted digital output signal, which is provided to theoutput interface 218.

In this embodiment, the analog signal path is taken from the output ofthe first amplifier circuitry 214 a of the first digital signal path,which may have additional analog buffer circuitry 224 similar to that ofthe embodiment of FIG. 4 to provide the analog microphone output signal.

Alternatively, the analog microphone output signal may be based on acombined version of the outputs of the first and second amplifiercircuitry 214 a,214 b of the digital signal paths. With reference to theembodiment illustrated in FIG. 5(b), the switchable microphone device210 b is configured such that the output of the first amplifiercircuitry 214 a and the output of the second amplifier circuitry 214 bare passed to the analog buffer circuitry 224, where the signals may becombined to provide a composite analog output for the interface 218.

It will be understood that the analog buffer circuitry 224 of FIG. 5(b)can be configured to implement an adjustable gain amplifier, signalcompression function, and/or an analog filtering module as describedabove with reference to the embodiment of FIG. 5(a).

In an effort to provide improved dynamic range performance, a switchablemicrophone device may be provided with multiple microphone transducerswherein each microphone transducer is tailored for a specific portion ofthe desired dynamic range. With reference to the embodiment illustratedin FIG. 5(c), the switchable microphone device 210 c comprises a firstmicrophone transducer 212 a configured or optimised to convert audioreceived within a first range of frequency and/or amplitude, and asecond microphone transducer 212 b configured or optimised to convertaudio received within a second range of frequency and/or amplitude.

It will be understood that the embodiment of FIG. 5(c) may be furtheradapted such that the output of both the first amplifier circuitry 214 aand second amplifier circuitry 214 b is combined in the analog buffercircuitry 224 to provide a composite analog output for the interface218. In addition, it will be understood that the analog buffer circuitry224 of FIG. 5(c) can be configured to implement an adjustable gainamplifier, signal compression function, and/or an analog filteringmodule as described above with reference to the embodiment of FIG. 5(a).

In a further aspect of the present disclosure, it will be understoodthat the microphone device 10,110,210 may be provided with an integrateddigital signal processing module (DSP) 17, which is indicated by adashed outline/box in FIG. 1, but may also be utilised in the otherembodiments of microphone device shown. The DSP 17 may be configured toperform some on-device signal processing of the converted digital signalbefore being output from the device. For example, the DSP 17 may beconfigured to perform one or more of the following:

-   -   noise reduction of the converted digital signal;    -   wind noise suppression of the converted digital signal;    -   filtration of the converted digital signal; and data formatting        of the digital signal.

As described above, the output interface may provide a multi-line ormulti-wire output from the device package.

Alternatively, the output interface 18,118,218 may provide a singleoutput pad or pin for the device package which may be switched betweenan analog or a digital output. An example of a first configuration ofsuch output interface is provided in FIG. 6. In FIG. 6, the outputinterface 18 comprises a digital signal node 30 coupled to the output ofthe digital signal path of the device, and an analog signal node 32coupled to the output of the analog signal path of the device. Inaddition, the output interface comprises the output pad 34. A switch 36is provided between the signal nodes 30,32 and the output pad 34, toselectively couple the respective digital signal node 30 and analogsignal node 32 with the output pad 34. Operation of the switch 36 iscontrolled by the device controller 20, which switches between thedigital or analog signal node 30,32, based on whether the device 10 isin the digital output mode or the analog output mode. It will beunderstood that the switch 36 may be implemented as suitabletransistors, e.g. MOSFETs.

An alternative configuration of the output interface 18 is provided inFIG. 7. In this embodiment, the interface comprises the digital signalnode 30 and analog signal node 32 and the output pad or pin 34 of FIG.6. The digital signal node 30 is connected to the output pad 34 througha first tri-state buffer 44. The analog signal node 32 is connected tothe output pad 34 through a second tri-state buffer 46. Theconfiguration of the respective first and second tri-state buffers 44,46is controlled by the controller 20.

When the device 10 is in the digital output mode, the first tri-statebuffer 44 is activated by the controller 20 to allow the digital outputsignal to pass through to the output pad 34. At the same time, thesecond tri-state buffer 46 is disabled by the controller 20, providing ahigh-impedance output of the buffer 46.

Similarly, when the device 10 is in the analog output mode, the firsttri-state buffer 44 is deactivated by the controller 20 to place thebuffer output in high-impedance mode, while the second tri-state buffer46 is activated to pass the analog output signal to the output pad 34.

It will be understood that the output pad 34 may comprise any suitablesolder pad or pin which may be provided on the device to allow output ofsignals from the device.

The switchable microphone device 10,110,210 is preferably provided aspart of a larger processing system. With reference to FIG. 8, an exampleimplementation of such a system 300 is shown. It will be understood thatthe system 300 may be provided as part of a larger electronic device301, e.g. a portable electronic device such as a mobile phone, a tabletcomputer, personal music player, or a smart device, such as a voiceassistant device, or an electronic device having embeddedvoice-processing functionality, e.g. a smart television, a home musicplayer or other home appliance.

A switchable microphone device 302 as described above is shown in FIG.8, which is arranged to provide an analog and/or a digital microphoneoutput signal. The switchable microphone device 302 is coupled with aprocessor unit 304, which may comprise an applications processor (AP) orcentral processing unit (CPU) for an electronic device. The processor304 is arranged to control the switching of the microphone device 302between the available output modes of the device 302, either bycontrolling the frequency of a clock signal provided to the device 302or by controlling a dedicated control signal provided to the device 302.

The system 300 further comprises an analog signal processing module 306and a digital signal processing module 308. It is recognised that as ananalog computing module can be relatively easily configured andoptimised for relatively low-power, always-on computing, and as adigital computing module can be relatively easily designed forrelatively high-performance, high-accuracy computing, the provision of ahybrid analog/digital computing system can provide considerableadvantages over prior art systems having only either an analog or adigital computing system. Preferably, the analog signal processingmodule 306 comprises an analog machine learning system, and preferablythe digital signal processing module 308 comprises a DSP or a digitalmachine learning system. Accordingly, the processor 304 is configured tocontrol the operation of the analog signal processing module 306 and thedigital signal processing module 308. In particular, the processor 304is arranged to switch the system 300 between:

-   -   an analog computing mode, wherein the microphone device 302 is        switched to the analog output mode to provide the analog        microphone output signal to the analog signal processing module        306; and    -   a digital computing mode, wherein the microphone device 302 is        switched to the digital output mode to provide the digital        microphone output signal to the digital signal processing module        308.

The processor 304 is further configured such that:

-   -   when in the analog computing mode, the processor 304 maintains        the digital signal processing module 308 in an inactive or        low-power state; and    -   when in the digital computing mode, the processor 304 maintains        the analog signal processing module 306 in an inactive or        low-power state.

Alternatively, the processor 304 may be configured to allow the analogsignal processing module 306 to remain active when in the digitalcomputing mode, to allow for processing of an analog output signal fromthe device 302, if the device 302 is configured to output the analogmicrophone output signal when in the digital output mode.

The processor 304 may switch the system 300 to the analog computing modewhen the device 301 is to be provided in a relatively low-power mode,e.g. in a standby or always-on-listening mode, which allows for theanalog signal processing module 306 to process the audio received by themicrophone device 302.

The processing performed by the analog signal processing module 306 maybe selected from one or more of the following:

-   -   a voice activity detection process (VAD) indicating the presence        of speech in received audio;    -   a voice keyword detection process (VKD) indicating the presence        of a keyword or wake-word in received audio;    -   a speaker identification or verification process indicating the        identity or authorisation of a speaker of the received audio;        and    -   a command recognition process arranged to recognise commands        present in speech in the received audio.

Once the analog signal processing module 306 detects that some activityhas occurred that may require additional processing power, e.g. themodule 306 provides a positive indication for one of the above-listedprocess, then the module 306 may notify the processor 304 accordingly,and/or provide the output 310 of the analog signal processing module 306to other downstream processing modules.

The processor 304 may then switch the system 300 to the digitalcomputing mode, thereby instructing the microphone device 302 to providea digital output signal and initialising or waking the digital signalprocessing module 308. The processor may also instruct the analog signalprocessing module 306 to transition to a low-power or inactive statewhen the system is in the digital computing mode. The digital signalprocessing module 308 may then perform digital system processing of thereceived audio, which may comprise a “second-pass” of the operationslisted above, and/or any further or additional signal processing of thereceived audio. The digital signal processing module 308 may then notifythe processor 304 of any outputs, and/or provide the output 312 of thedigital signal processing module 308 to other downstream processingmodules.

Additionally or alternatively, the processor 304 may be configured totransition to the digital computing mode based on any other input, e.g.an external user input indicating that the device 301 is to change froman inactive to an active state, or an indication that the device 301 isoperating on mains power or with a relatively high level of batterypower.

The processor 304 may be configured to switch the system 300 back to theanalog computing mode, i.e. instructing the microphone device 302 toprovide an analog output signal, while initialising or waking the analogsignal processing module 306 and/or instructing the digital signalprocessing module 308 to transition to a low-power or inactive state.The transition to the analog computing mode may be triggered by anysuitable input, e.g. a user input such as an indication to power-downthe system 301; the processor 304 determining that a user interactionsession has ended or that a session has timed-out; or a relatively lowlevel of battery power for the device 301.

By providing a system that can switch between analog and digitalcomputing modes, a device can be provided with the reduced powerconsumption of an analog-computing-based always-on listening mode andthe high-accuracy processing of a digital-computing-based mode whenrequired.

In a further aspect, the processor 304 may allow for the switching ofthe system to a hybrid computing mode, where the microphone device 302is switched to a hybrid output mode to simultaneously provide the analogmicrophone output signal to the analog signal processing module 306, andto provide the digital microphone output signal to the digital signalprocessing module 308. The use of a hybrid processing module may allowfor the analog and digital modules 306,308 to operate in parallel. Theoutputs 310,312 of the modules may then be fused or combined to provideimproved accuracy.

In the embodiment of FIG. 8, the analog and digital modules 306,308 areconnected to the same pin or bus output of the switchable microphonedevice 302. It will further be understood that, as described above, theswitchable microphone device 302 may be provided with separate analogand digital outputs, wherein the analog signal processing module 306 isconnected to an analog output of device 302 and the digital signalprocessing module 308 is connected to a digital output of device 302.

In the embodiment of FIG. 8, the processor 304 is shown as a separateelement to the analog and digital modules 306,308, e.g. as separateintegrated circuit devices. Alternatively, it will be understood thatone or more of the modules 306,308 may be provided integrally as part ofthe processor unit 304.

In an alternative aspect, it will be understood that the system of FIG.8 may be provided with analog and digital microphone output signals fromalternative microphone devices, e.g. from a dedicated analog microphoneand a dedicated digital microphone, wherein the dedicated analogmicrophone may be powered-down or made inactive during a digitalcomputing mode, and wherein the dedicated digital microphone may bepowered-down or made inactive during an analog computing mode.

The switchable microphone device 10/110/210 described above typicallyproduces an output digital signal of relatively limited bandwidth at theoutput interface 18, due to limitations of the ADC 16. For example, ifthe ADC 16 receives a clock signal at a frequency of 768 kHz (whichclock signal frequency may be selected based on an audio signalbandwidth of 16 kHz and a 48 x oversampling rate), the usable bandwidthof the converted digital signal output by the ADC 16 may beapproximately 8 kHz. This usable signal bandwidth is sufficient forapplications requiring limited signal bandwidth such as detectingspeech, but is not sufficient for detecting signals of higher bandwidth.

In some applications it may be desirable to be able to detect andprocess signals of higher bandwidth. For example, in some applicationssignal content at ultrasonic signal frequencies may contain usefulinformation.

For example, voice assistants or voice biometric systems can bevulnerable to so-called “spoofing” or “replay” attacks, in which arecording or other reproduction of an authorised user's voice is playedto the voice assistant or voice biometric system by somebody other thanthe authorised user in an attempt to gain access to a voice interface ofthe voice assistant or voice biometric system.

It has also been found that it is possible to gain access to a voiceinterface using audio encoded in the ultrasonic frequency band(sometimes referred to as a “dolphin attack”). Because such attacks useultrasonic frequencies, they cannot easily be detected by a human user.

Further, the performance of voice assistants and voice biometric systemscan be adversely affected by ultrasonic interference. Such interferencemay arise, for example, from ultrasonic sources such as ultrasonicmotion detectors.

Thus, it may be desirable to be able to detect and process signalshaving a bandwidth greater than the usable bandwidth of the digitalmicrophone output signal output by the switchable microphone device, orthe usable bandwidth of the converted digital signal output by theswitchable microphone device 10/110/210, such as ultrasonic signals, inorder to detect malicious attacks on voice assistants or voice biometricsystems, or to detect interference that could degrade the performance ofa voice assistant or voice biometric system.

One way to increase the usable bandwidth of converted digital signaloutput by the switchable microphone device 10/110/210 (and thus theusable bandwidth of the digital microphone output signal output by theswitchable microphone device) would be to increase the frequency of theclock signal received by the ADC 16. However, this may not be possible,because the digital microphone output signal and/or the converteddigital signal may need to be shared between multiple different devicesor subsystems, which may not be able to accommodate dynamic adjustmentof the frequency of the clock signal supplied to the ADC 16 and theconsequential change in the bandwidth of the converted digital signaland the digital microphone output signal.

With reference to FIG. 10, a further example implementation of a systemincorporating a switchable microphone device of the kind described aboveis shown generally at 1000. It will be understood that the system 1000may be provided as part of a larger host electronic device 1010, e.g. aportable electronic device such as a mobile phone, a tablet computer,personal music player, or a smart device, such as a voice assistantdevice, or an electronic device having embedded voice-processingfunctionality, e.g. a smart television, home music player or other homeappliance.

The switchable microphone device 1020 is coupled with a first processorunit or controller 1030, which may comprise, for example, a centralprocessing unit (CPU) of a host electronic device. The first processorunit 1030 is arranged to control the switching of the microphone device1020 between the available output modes of the device 1020, either bycontrolling the frequency of a clock signal provided to the device 1020or by controlling a dedicated control signal provided to the device1020.

The system 1000 also includes a second processor unit 1040 downstream ofthe switchable microphone device 1020. The second processor unit 1040may be, for example, a codec, an applications processor of the hostdevice 1010 or the like. Although for clarity the second processor unit1040 is shown as being separate from the first processor unit 1030, itis to be appreciated that the functionality of the first and secondprocessor units 1030, 1040 could be integrated in a single processorunit. For example, the first processor unit 1030 may also include theelements of the second processor unit 1040 described below, and thus mayimplement the functionality of the second processor unit 1040 describedbelow.

The analog output of the interface unit of the switchable microphonedevice 1020 is coupled to an analog input of the second processingdevice 1040 such that the second processing device 1040 receives theanalog microphone output signal output by the switchable microphonedevice 1020. The digital output of the interface unit of the switchablemicrophone device 1020 may be coupled to a digital input of the secondprocessing device 1040 such that the second processing device 1040receives the digital microphone output signal output by the switchablemicrophone device 1020.

The second processor unit 1040 includes an analog to digital converter(ADC) 1042 (which may be referred to as a second ADC, to distinguish itfrom the ADC 16 of the switchable microphone device). The second ADC1042 is coupled to the analog input of the second processor unit 1040 soas to receive the analog signal output by the switchable microphonedevice. The second ADC 1042 is configured to provide a supplementary orsecond converted digital output signal with a higher usable bandwidththan the digital microphone output signal output by the switchablemicrophone device 1020. Thus, the ADC 1042 of the second processor unit1040 has a higher bandwidth than the ADC 16 of the switchable microphoneunit 1020, such that, for example, ultrasonic signal content in theanalog signal output by the amplifier circuitry 14 of the switchablemicrophone unit 1020 is retained in the supplementary converted digitalsignal output by the ADC 1042. To this end, the ADC 1042 may receive aclock signal at a higher frequency than that of a clock signal that issupplied to the ADC 16 of the switchable microphone unit 1020. Forexample, in order for the second ADC 1042 to retain ultrasonic signalcontent at frequencies up to 40 kHz, the frequency of the clock signalsupplied to the second ADC 1042 may be of the order of 3.84 MHz.

The ADC 1042 is normally disabled, but can be enabled when thesupplementary (high-bandwidth) converted digital signal is desired. Forexample, an enable signal EN can be transmitted by the controller 1030to the ADC 1042 to enable the ADC 1042 when the converted digital outputsignal output by the ADC 16 of the switchable microphone device 1020(which may be referred to as the first converted digital output signal)or the digital microphone output signal is indicative that particularaudio content such as speech or a trigger word or phrase (e.g. “heySiri”, “OK Google”, “Alexa”, etc.) intended to wake up a voice assistantof voice biometric system has been detected.

When the ADC 1042 is enabled, the analog signal output by the switchablemicrophone device 1020 is converted into a high-bandwidth supplementaryconverted digital output signal by the ADC 1042. This high-bandwidthsupplementary converted digital output signal contains higher frequencysignal content than the digital microphone output signal output by theswitchable microphone device 1020. For example, the high-bandwidthsupplementary converted digital output signal output by the ADC 1042 mayinclude ultrasonic frequency signal content of the analog signal outputby the switchable microphone device 1020 that is not retained in thedigital microphone output signal.

In some examples the bandwidth of the high-bandwidth supplementaryconverted digital output signal is complementary to the bandwidth of thedigital microphone output signal output by the switchable microphonedevice 1020 when the digital microphone device 1020 is operating in thehybrid mode described above, in which both a digital microphone outputsignal and an analog microphone output signal are output by theswitchable microphone device. For example, if the digital microphoneoutput signal contains frequencies in the range 0 Hz-8 kHz, then thesupplementary converted digital output signal may contain frequencies inthe range 8 kHz-40 kHz. The second processor unit 1040 may include acombiner or adder 1044 which is configured to combine the supplementaryconverted digital output signal with the digital microphone outputsignal so as to generate a full-bandwidth digital signal that can beoutput to one or more further downstream digital processing modules forfurther processing. The supplementary converted digital output signalmay be filtered and/or otherwise processed, e.g. by a filter submoduleand/or other processing submodule that may be provided as part of thesecond processor unit 1040 or external to the second processor unit1040, prior to being combined with the digital microphone output signalin order match the signal gain of the supplementary converted digitaloutput signal with that of the lower bandwidth digital microphone outputsignal to generate the full bandwidth digital signal.

In other examples, the bandwidth of the supplementary converted digitaloutput signal may encompass the bandwidth of the digital microphoneoutput signal when the digital microphone device 1020 is operating inthe hybrid mode described above, (e.g. if the digital microphone outputsignal contains frequencies in the range 0 Hz-8 kHz, then thesupplementary converted digital output signal may contain frequencies inthe range 0 Hz-40 kHz), in which case combining the supplementaryconverted digital signal with the digital microphone output signal isnot necessary, and the supplementary converted digital signal can beoutput to the further downstream digital processing module(s) as thefull-bandwidth digital signal for further processing.

In other examples, where it is expected that the switchable microphonedevice 1020 will not operate in the hybrid mode described above, thebandwidth of the ADC 1042 of the second processor unit 1040 may beconfigured such that the bandwidth of the supplementary converteddigital output signal encompasses the bandwidth of the digitalmicrophone output signal (e.g. if the digital microphone output signalcontains frequencies in the range 0 Hz-8 kHz, then the supplementaryconverted digital output signal may contain frequencies in the range 0Hz-40 kHz), such that the second processor unit 1040 is able to output afull bandwidth digital signal for further processing by the downstreamdigital processing module(s) even when the switchable microphone device1020 is not able to operate in the hybrid mode described above.

Processing of the full-bandwidth digital signal by the furtherdownstream digital processing module(s) may identify that no ultrasonicfrequency signal content is present in the full-bandwidth digitalsignal. This may be indicative of an attempted spoofing or replayattack, since ultrasonic frequency content would usually be expected ina genuine voice command such as a trigger word or phrase. Thus, thefurther downstream digital processing module(s) can take appropriateaction such as issuing an alert or signal to prevent access to a voiceinterface of the host device 1010.

Processing of the full-bandwidth digital signal by the furtherdownstream digital processing module(s) may identify that ultrasonicfrequency signal content is present in the full-bandwidth digitalsignal. This may be indicative of an attempted dolphin attack insituations in which no voice audio signal has been detected. Thus, thedownstream digital processing module(s) can take appropriate action suchas issuing an alert or signal to prevent access to a voice interface ofthe host device 1010.

The presence of ultrasonic frequency signal content in thefull-bandwidth digital signal may, additionally or alternatively, beindicative of the presence of ultrasonic interferers which couldcompromise the performance of a voice assistant or voice biometricsystem. For example, if ultrasonic frequency signal content atparticular frequencies (e.g. 40 kHz) that are typically used byultrasonic devices such as motion detectors such as 40 kHz is detectedby the downstream digital processing module(s) as well as audio signalcontent such as speech, the downstream digital processing module(s) maytake appropriate action such as flagging the audio signal content asbeing potentially affected by ultrasonic interference, so thatadditional processing to mitigate the possible interference can beperformed when processing the audio content.

In some examples the second processor unit 1040 may include an analogsignal buffer 1046 for storing the analog signal output by theswitchable microphone device 1020 over a predetermined period of time.For example, the analog signal buffer 1046 may store the last 10seconds' worth of the analog signal output by the switchable microphonedevice 1020, such that when the ADC 1042 is enabled by the firstprocessor unit 1030 (in response to detection of a particular audiosignal such as speech or a trigger word or phrase) the ADC 1042 cangenerate a high-bandwidth supplementary converted digital signal basedon the analog signal stored in the buffer 1046. Thus, high-bandwidthsignal content from the period immediately before the ADC 1042 wasenabled can be processed, e.g. to identify possible attacks orinterference as described above. The switchable microphone device 1020may similarly generate a digital microphone output signal based on ananalog signal stored over the predetermined period of time in a similaranalog signal buffer that may be provided as part of the switchablemicrophone device 1020. This digital microphone output signal based onthe buffered analog signal can be combined with the high-bandwidthsupplementary converted digital signal generated by the ADC 1042 basedon the buffered analog microphone output signal in order to generate afull-bandwidth digital signal for the period immediately before the ADC1042 was enabled, which can be processed as described above e.g. toidentify possible attacks or interference.

The system 1000 thus permits high-bandwidth signal content that cannotbe retained in the digital microphone output signal to be retained andprocessed by downstream digital processing modules in order to detectattacks, interference and the like.

With reference to FIG. 11, a further embodiment of a switchablemicrophone device 1100 according to the present disclosure is shown. Theswitchable microphone device 1100 is able to provide a converted digitaloutput signal of a higher bandwidth than the converted digital signaloutput by the switchable microphone device 10/110/210.

The switchable microphone device 1100 is similar to the switchablemicrophone device 10 of FIG. 1, and so elements that are common to boththe switchable microphone device 10 and the switchable microphone device1100 are denoted by common reference numerals. Such common elementsoperate in the manner described above with reference to FIG. 1, and sowill not be described in detail here.

As in the switchable microphone device 10, the switchable microphonedevice 1100 of FIG. 11 includes a first ADC 16, which converts an analogsignal received from the amplifier circuitry 14 into a first converteddigital output signal. The first ADC 16 in this example is a relativelylow bandwidth ADC. For example, the first ADC 16 may receive a clocksignal at a frequency of 768 kHz, giving rise to a usable bandwidth ofthe converted digital signal output by the first ADC 16 of approximately8 kHz as discussed above.

The switchable microphone device 1100 also includes a second ADC 1102,which is provided in the analog signal path between the output of theamplifier circuitry 14 and the output interface 18. The second ADC 1102is configured to provide a second converted digital output signal with ahigher usable bandwidth than the first converted digital signal outputby the ADC 16 (i.e. the second ADC 1102 has a higher bandwidth than thefirst ADC 16), such that, for example, ultrasonic signal content in theanalog signal output by the amplifier circuitry 14 is retained in thesecond converted digital signal output by the second ADC 1002. To thisend, the second ADC 1102 may receive a clock signal at a higherfrequency than that of a clock signal that is supplied to the first ADC16. For example, in order for the ADC 1102 to retain ultrasonic signalcontent at frequencies up to 40 kHz, the frequency of the clock signalsupplied to the second ADC 1102 may be of the order of 3.84 MHz.

The second ADC 1102 is normally disabled, such that the analog signalpath provides an analog signal to the output interface 18, as describedabove. The second ADC 1102 can be enabled when the second(high-bandwidth) converted digital signal is desired. For example, anenable signal EN can be transmitted by the controller 20 or by aprocessor of a host device incorporating the microphone device 1000 tothe second ADC 1102 to enable the second ADC 1102 when the firstconverted digital output signal output by the first ADC 16 is indicativethat particular audio content such as speech or a trigger word or phrase(e.g. “hey Siri”, “OK Google”, “Alexa”, etc.) intended to wake up avoice assistant of voice biometric system has been detected.

When the second ADC 1102 is enabled, the analog signal output by theamplifier circuitry 14 is converted into a high-bandwidth secondconverted digital output signal by the second ADC 1002. Thishigh-bandwidth second converted digital output signal contains higherfrequency signal content than the first converted digital output signaloutput by the first ADC 16. For example, the high-bandwidth secondconverted digital output signal output by the second ADC 1102 mayinclude ultrasonic frequency signal content of the analog signal outputby the amplifier circuitry 14 that is not retained in the firstconverted digital output signal output by the first ADC 16.

The high-bandwidth second converted digital output signal is output bythe second ADC 1102 to the output interface 18.

In some examples the bandwidth of the high-bandwidth second converteddigital output signal is complementary to the bandwidth of the firstconverted digital output signal. For example, if the first converteddigital output signal contains frequencies in the range 0 Hz-8 kHz, thenthe second converted digital output signal may contain frequencies inthe range 8 kHz-40 kHz. The switchable microphone device 1000 mayinclude a combiner or adder 1004 which is configured to combine thefirst and second converted digital output signals so as to generate afull-bandwidth digital signal that can be output to one or moredownstream digital processing modules for further processing (afterappropriate filtering and/or other processing of the second converteddigital output signal if necessary by, e.g. a filter submodule and/orother processing submodule that may be provided as part of theswitchable microphone device 1100, in order match the signal gain of thesecond converted digital output signal with that of the lower bandwidthfirst converted digital output signal to generate the full bandwidthdigital signal).

Although the combined or adder 1104 is shown in the illustrated exampleas being provided as part of the output interface, those skilled in theart will appreciate that the combiner/adder 1104 could be provided atany other convenient location in the switchable microphone device 1100.

In other examples, the bandwidth of the second converted digital outputsignal may encompass the bandwidth of the first digital output signal(e.g. if the first converted digital output signal contains frequenciesin the range 0 Hz-8 kHz, then the second converted digital output signalmay contain frequencies in the range 0 Hz-40 kHz), in which casecombining the first and second converted digital signals is notnecessary, and the second converted digital signal can be output to thedownstream digital processing module(s) as the full-bandwidth digitalsignal for further processing.

Processing of the full-bandwidth digital signal by the downstreamdigital processing module(s) may identify that no ultrasonic frequencysignal content is present in the full-bandwidth digital signal. This maybe indicative of an attempted spoofing or replay attack, sinceultrasonic frequency content would usually be expected in a genuinevoice command such as a trigger word or phrase. Thus, the downstreamdigital processing module(s) can take appropriate action such as issuingan alert or signal to prevent access to a voice interface of a hostdevice incorporating the switchable microphone device 1100 and thedownstream digital processing module(s).

Processing of the full-bandwidth digital signal by the downstreamdigital processing module(s) may identify that ultrasonic frequencysignal content is present in the full-bandwidth digital signal. This maybe indicative of an attempted dolphin attack in situations in which novoice audio signal has been detected. Thus, the downstream digitalprocessing module(s) can take appropriate action such as issuing analert or signal to prevent access to a voice interface of a host deviceincorporating the switchable microphone device 1100 and the downstreamdigital processing module(s).

The presence of ultrasonic frequency signal content in thefull-bandwidth digital signal may, additionally or alternatively, beindicative of the presence of ultrasonic interferers which couldcompromise the performance of a voice assistant or voice biometricsystem. For example, if ultrasonic frequency signal content atparticular frequencies (e.g. 40 kHz) that are typically used byultrasonic devices such as motion detectors such as 40 kHz is detectedby the downstream digital processing module(s) as well as audio signalcontent such as speech, the downstream digital processing module(s) maytake appropriate action such as flagging the audio signal content asbeing potentially affected by ultrasonic interference, so thatadditional processing to mitigate the possible interference can beperformed when processing the audio content.

In some examples the switchable microphone device 1100 may include ananalog signal buffer 1106 for storing the analog signal output by theamplifier circuitry 14 over a predetermined period of time. For example,the analog buffer 1106 may store the last 10 seconds' worth of theanalog signal output by the amplifier circuitry 14, such that when thesecond ADC 1102 is enabled by the controller 20 (in response todetection of a particular audio signal such as speech or a trigger wordor phrase) the second ADC 1102 can generate a high-bandwidth secondconverted digital signal based on the analog signal stored in the buffer1106, such that high-bandwidth signal content from the periodimmediately before the second ADC 1002 was enabled can be processed,e.g. to identify possible attacks or interference as described above.The first ADC 16 may similarly generate a first converted digital outputsignal based on the analog signal stored in the buffer 1006, which canbe combined with the high-bandwidth second converted digital signalgenerated by the second ADC 1002 based on the buffered analog signal inorder to generate a full-bandwidth digital signal for the periodimmediately before the second ADC 1102 was enabled, which can beprocessed as described above e.g. to identify possible attacks orinterference.

The switchable microphone device 1100 thus permits high-bandwidth signalcontent that cannot be retained in the digital microphone output signalto be retained in the second digital output signal and made availablefor processing by downstream digital processing modules in order todetect attacks, interference and the like.

While the above-described features relate to a microphone device and thesignals produced by microphone transducers, it will be understood thatthe same principles and features may be applied for alternative devices,having other types of transducers where it may be desired to provideswitchable analog and digital output modes, for example opticaltransducers, capacitive transducers, force sensing transducers,inductive sensing transducers, proximity detection transducers,ultrasonic transducers. With reference to FIG. 9, the embodiment of FIG.1 is reproduced with a general transducer 13 replacing the microphonedevice 10 of FIG. 1. It will be understood that the above description offeatures for the embodiment of FIG. 1 may equally apply to the featuresof the embodiment of FIG. 9, mutatis mutandis.

The invention is not limited to the embodiments described herein, andmay be modified or adapted without departing from the scope of thepresent invention.

The invention claimed is:
 1. A switchable microphone device comprising:an input to receive an input analog sensor signal indicative of soundpressure received by a transducer; an analog-to-digital converter (ADC)to convert the input analog sensor signal to a converted digital signal;and a controller to switch the device between: a digital output mode,wherein the switchable microphone device outputs a digital microphoneoutput signal based on the converted digital signal; and an analogoutput mode, wherein the switchable microphone device outputs an analogmicrophone output signal based on the input analog sensor signal,wherein the switchable microphone device outputs the analog microphoneoutput signal when the device is in the digital output mode.
 2. Thedevice of claim 1, further comprising at least one microphone transducerconfigured to provide the input analog sensor signal indicative of soundpressure received by the at least one microphone transducer.
 3. Thedevice of claim 1, wherein the device is arranged to receive a controlsignal, wherein the controller switches between the digital and analogoutput modes based on the received control signal.
 4. The device ofclaim 1, wherein the controller is further configured to switch thedevice to: a hybrid output mode, wherein the switchable microphonedevice outputs both the digital microphone output signal based on theconverted digital signal, and the analog microphone output signal basedon the input analog sensor signal.
 5. The device of claim 1, wherein thedevice is arranged to receive a clock signal, wherein the clock signaloperates as the control signal to control the switching of the outputmodes of the device.
 6. The device of claim 5, wherein the controller isarranged to monitor the received clock signal, wherein the controllerswitches the device to the analog output mode if the clock signal isretained at a high value or at a low value exceeding a threshold timeperiod.
 7. The device of claim 5, wherein the controller is configuredto switch the device to the digital output mode if the received clocksignal is within an allowed frequency range.
 8. The device of claim 1,wherein the device is provided with a control input, wherein the controlinput controls the switching of the output modes of the device.
 9. Thedevice of claim 1, wherein the device further comprises amplifiercircuitry to provide a buffered analog output signal based on the inputanalog sensor signal.
 10. The device of claim 9, wherein the amplifiercircuitry comprises one or more of the following: an adjustable gainamplifier; a signal compression function; or an analog filtering module.11. The device of claim 1, wherein the device further comprises anoutput interface to provide a digital microphone output signal based onthe converted digital signal.
 12. The device of claim 1, wherein thedevice further comprises a digital signal processing module arranged toperform digital signal processing on the converted digital signal toprovide a processed digital signal, and wherein the digital microphoneoutput signal is based on the processed digital signal.
 13. The deviceof claim 1, wherein the device comprises: a digital output interface tooutput the digital microphone output signal; and an analog outputinterface to output the analog microphone output signal.
 14. The deviceof claim 13, wherein the device comprises a common output pin, whereinthe controller controls the driving of the common output pin by thedigital output interface and the analog output interface.
 15. The deviceof claim 13, wherein the digital output interface comprises a digitalbus, such as a single-wire or multiple-line bus, and wherein the analogoutput interface comprises at least one analog output pin, and whereinthe at least one analog output pin is separate from the digital bus. 16.The device of claim 1, wherein the device comprises a plurality ofdigital signal paths for the input analog sensor signal to provide aconverted digital signal having a high dynamic range, the digital signalpaths each comprising an amplifier circuitry and an ADC, wherein theamplifier circuitry of the different paths is configured to providedifferent signal ranges of the input analog sensor signal, and whereinthe outputs of the ADCs of the different paths are combined to provide aconverted digital signal having a high dynamic range.
 17. The device ofclaim 16, wherein the analog microphone output signal is based on acombined version of the outputs of the amplifier circuitry of thedifferent paths.
 18. The device of claim 16, wherein the analogmicrophone output signal is based on the output of the amplifiercircuitry of one of the digital signal paths.
 19. A system comprising: aswitchable microphone device as claimed in claim 1; and a processorconfigured to control switching of the microphone device between thedigital output mode and the analog output mode.
 20. The system of claim19, wherein the processor controls a clock signal provided to themicrophone device to control the mode switching of the microphonedevice, or the processor controls a control signal provided to themicrophone device to control the mode switching of the microphonedevice.
 21. The system of claim 19, wherein the system furthercomprises: an analog signal processing module, the analog signalprocessing module arranged to receive an analog microphone output signalfrom the switchable microphone device; and a digital signal processingmodule, the digital signal processing module arranged to receive adigital microphone output signal from the switchable microphone device.22. The system of claim 21, wherein the processor is arranged to switchthe system between: an analog computing mode, wherein the microphonedevice is switched to the analog output mode to provide the analogmicrophone output signal to the analog signal processing module; and adigital computing mode, wherein the microphone device is switched to thedigital output mode to provide the digital microphone output signal tothe digital signal processing module.
 23. The system of claim 22,wherein the system is further configured such that: when in the analogcomputing mode, the processor is configured to maintain the digitalsignal processing module in an inactive or low-power state; and when inthe digital computing mode, the processor is configured to maintain theanalog signal processing module in an inactive or low-power state. 24.The system of claim 22, wherein the switchable microphone devicecontinues to output an analog microphone output signal when theswitchable microphone device is switched to the digital output mode, thesystem is configured such that: when in the analog computing mode, theprocessor is configured to maintain the digital signal processing modulein an inactive or low-power state; and when in the digital computingmode, the processor is configured to activate both to maintain theanalog signal processing module and the digital signal processingmodule.
 25. The system of claim 22, wherein the processor is arranged tofurther switch the system to: a hybrid computing mode, wherein themicrophone device is switched to a hybrid output mode to provide theanalog microphone output signal to the analog signal processing module,and to provide the digital microphone output signal to the digitalsignal processing module.
 26. The system of claim 22, wherein theprocessor switches the system from the analog computing mode to thedigital computing mode based on one or more of the following: a userinput, such as a mechanical button press; a voice activity detectionmodule (VAD) indicating the presence of speech in received audio; avoice keyword detection module (VKD) indicating the presence of akeyword or wake-word in received audio; a speaker identification orverification module indicating the identity or authorisation of aspeaker of the received audio; a command recognition module arranged torecognise commands present in speech in the received audio.
 27. Thesystem of claim 22, wherein the processor switches the system from thedigital computing mode to the analog computing mode based on one or moreof the following: a user input, e.g. an indication to power-down thesystem; the processor determining that a session has ended; and a systemtime-out.
 28. An electronic device comprising the system of claim 22,the electronic device comprises a portable electronic device such as amobile phone, a tablet computer, personal music player, or wherein theelectronic device comprises a smart device, such as a voice assistantdevice, or an electronic device having embedded voice-processingfunctionality, such as a smart television or other home appliance, ahome music player.
 29. A system comprising: at least one microphonedevice to provide a microphone signal indicative of sound pressurereceived by a transducer of the microphone; an analog signal processingmodule, the analog signal processing module arranged to receive ananalog microphone signal from a microphone device; a digital signalprocessing module, the digital signal processing module arranged toreceive a digital microphone signal from a microphone device; and aprocessor arranged to control switching of the system between: an analogcomputing mode, wherein the analog signal processing module is enabledand the digital signal processing module is maintained in a low-power orinactive state; and a digital computing mode, wherein the digital signalprocessing module is enabled and the analog signal processing moduleremains in an active state.
 30. The system of claim 29, wherein theanalog and digital signal processing modules are arranged to processaudio received by a microphone transducer.
 31. The system of claim 29,wherein the analog and digital signal processing modules may beconfigured to perform one or more of the following: a voice activitydetection process (VAD) indicating the presence of speech in receivedaudio; a voice keyword detection process (VKD) indicating the presenceof a keyword or wake-word in received audio; a speaker identification orverification process indicating the identity or authorisation of aspeaker of the received audio; a speech recognition process arranged torecognise speech in the received audio; and a command recognitionprocess arranged to recognise commands present in speech in the receivedaudio.
 32. The system of claim 29, wherein the analog signal processingmodule comprises an analog machine learning system, preferably whereinthe analog signal processing module is configured for relativelylow-power, always-on computing.
 33. The system of claim 29, wherein thedigital signal processing module comprises a digital machine learningsystem, preferably wherein the digital signal processing module isconfigured for relatively high-performance, high-accuracy computing. 34.The system of claim 29, wherein the processor is arranged to furthercontrol switching of the system between: a hybrid computing mode,wherein both the analog signal processing module and the digital signalprocessing module are enabled.
 35. A switchable transducer devicecomprising: an input to receive an input analog sensor signal from atransducer; an analog-to-digital converter (ADC) to convert the inputanalog sensor signal to a converted digital signal; and a controller toswitch the device between: a digital output mode, wherein the switchabletransducer device outputs a digital output signal based on the converteddigital signal; and an analog output mode, wherein the switchabletransducer device outputs an analog output signal based on the inputanalog sensor signal, wherein the switchable transducer device outputsthe analog sensor signal when the device is in the digital output mode.36. A system comprising: a switchable transducer device as claimed inclaim 35; and a processor configured to control switching of thetransducer device between the digital output mode and the analog outputmode, the processor arranged to control processing of the output of thetransducer device.